Random and localized resistive switching observation in Pt/NiO/Pt (original) (raw)
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Effects of metal electrodes on the resistive memory switching property of NiO thin films
Applied Physics Letters, 2008
The effects of various metal electrodes on the resistive switching of NiO thin films were investigated. Contrary to the belief that Pt is used for its high work function, which enables Ohmic contact to p-type NiO, resistive switching was observed in films with Ta or Al electrodes with a low work function in the as-deposited state. The resistive switching of films with a Ag or Cu top electrode with a low work function and high free energy of oxidation shows the importance of the formation of an oxide layer at the metal/NiO interface.
Atomic structure of conducting nanofilaments in TiO2 resistive switching memory
Nature Nanotechnology, 2010
Resistance switching in metal oxides could form the basis for next-generation non-volatile memory. It has been argued that the current in the high-conductivity state of several technologically relevant oxide materials flows through localized filaments, but these filaments have been characterized only indirectly, limiting our understanding of the switching mechanism. Here, we use high-resolution transmission electron microscopy to probe directly the nanofilaments in a Pt/TiO 2 /Pt system during resistive switching. In situ current-voltage and low-temperature (130 K) conductivity measurements confirm that switching occurs by the formation and disruption of Ti n O 2n21 (or so-called Magnéli phase) filaments. Knowledge of the composition, structure and dimensions of these filaments will provide a foundation for unravelling the full mechanism of resistance switching in oxide thin films, and help guide research into the stability and scalability of such films for applications.
Resistive Random Access Memory (RRAM) with a structure Au/Ti/TiO 2−x /Au demonstrated a clear bipolar resistive switching behavior without the necessity of an initial electroforming process. The titanium oxide (TiO 2−x ) thin film was deposited by reactive RF magnetron sputtering at room temperature in a controlled oxygen/argon ambient. The high density of oxygen vacancies within the film (induced by the low oxygen content) is an essential component for the formation of conducting filaments and demonstration of DC or nanosecond pulsed resistance switching, but also impose limitations for the conduction behavior of the high resistance state. Conductive Atomic Force Microscopy (C-AFM) was then employed in order to investigate the nanoscale electrical properties of our device. In situ current distribution during the SET process disclosed possible formation of conducting filaments while DC sweeping bias voltage revealed an OFF/ON switching ratio of about 200. We have also demonstrated that by using C-AFM both a low resistance state and a high resistance state can be written by bipolar voltage application imaged by corresponding patterns on the TiO 2−x current image, suggesting that oxygen ions movement at the Pt-Ir coated tip/TiO 2−x interface plays a critical role in the resistive switching phenomenon and thus correlating the macroscopic characteristics of our device with its microscopic origins. Nanoscale resistance switching is also demonstrated by programming distinct patterns on the device's current image.
Occurrence of Both Unipolar Memory and Threshold Resistance Switching in a NiO Film
Physical Review Letters, 2009
We observed two types of unipolar resistance switching (RS) in NiO film: memory RS at low temperature and threshold RS at high temperature. We explain these phenomena using a bond percolation model that describes the forming and rupturing of conducting filaments. Assuming Joule heating and thermal dissipation processes in the bonds, we explain how both RS types could occur and be controlled by temperature. We show that these unipolar RS are closely related and can be explained by a simple unified percolation picture.
Nonpolar resistive switching in the Pt/MgO/Pt nonvolatile memory device
Applied Physics Letters, 2010
Nonpolar resistive switching ͑RS͒, which is the coexistence of unipolar and bipolar RS characteristics, in the Pt/MgO/Pt memory device with the nonforming nature is demonstrated. The nonforming nature is ascribed to the relatively high defect density of the MgO film deposited by using the ion beam sputtering in Ar atmosphere. The results of Auger electron spectroscopy and x-ray photoelectron spectroscopy analyses combing with the temperature dependence of resistance suggest that metallic Mg filaments are formed in the low resistance state. The voltage-polarity-independent RESET process implies that filaments may be ruptured by local Joule heating, leading to nonpolar characteristics.
Advanced Functional Materials, 2014
Although the kinetics of CF formation/ dissolution is still unclear, it is widely accepted that the CF formation/dissolution is strongly related to the electromigration and electrochemical reaction of anion (i.e., oxygen vacancy) or cation (i.e., Cu 2+ , Ag + or Ni 2+ ). Generally, RS behavior can be classifi ed as two modes: nonvolatile memory switching (MS) and volatile threshold switching (TS). In the MS mode, both LRS and HRS can be maintained after removing the external voltage, while the LRS in the TS mode will be back to the HRS once the applied voltage is smaller than a critical value. To avoid confusion with MS, the LRS and HRS in TS are renamed as "TS ON-state" and "TS OFFstate" in this article. The MS device can be used for the non-volatile data storage while TS device can be as a selector in series with memory cell to suppress crosstalk effect in the crossbar array. Recently, some groups reported that TS and MS can coexist and mutually transform in a single device at suitable external excitation. Several models have been proposed to explain this phenomenon, including CF thermal instability, strong electron correlation effect, quantum-wire model, interface barrier modulation, and space charge effect. However, the underlying mechanism of the phenomenon is still unclear, especially lacking of direct evidences to uncover when and how the two RS modes happen and what is the internal relationship between them.
Electrical Manipulation of Nanofilaments in Transition-Metal Oxides for Resistance-Based Memory
Nano Letters, 2009
The fabrication of controlled nanostructures such as quantum dots, nanotubes, nanowires, and nanopillars has progressed rapidly over the past 10 years. However, both bottom-up and top-down methods to integrate the nanostructures are met with several challenges. For practical applications with the high level of the integration, an approach that can fabricate the required structures locally is desirable. In addition, the electrical signal to construct and control the nanostructures can provide significant advantages toward the stability and ordering. Through experiments on the negative resistance switching phenomenon in Pt-NiO-Pt structures, we have fabricated nanofilament channels that can be electrically connected or disconnected. Various analyses indicate that the nanofilaments are made of nickel and are formed at the grain boundaries. The scaling behaviors of the nickel nanofilaments were closely examined, with respect to the switching time, power, and resistance. In particular, the 100 nm × 100 nm cell was switchable on the nanosecond scale, making them ideal for the basis for high-speed, high-density, nonvolatile memory applications.
physica status solidi (a), 2018
In this work, the authors present a study of the resistive switching effect (RS) in Co 0.2 TiO 3.2 (CTO) in a thin film structure Pt/CTO/ITO. The identification of a structure of low crystallinity with different deposition times is seen in the diffractograms with a certain tendency of orientation in the plane (311) of the inverted spinel of space group Fd-3m. Electrical measurements I-V highlight the appearance of RS effect predominated by unipolar filamentary mechanism. The retention of charge in the device shows good stability and separation of HRS-LRS states with R OFF /R ON %10 6 ratio. The authors are able to demonstrate that Co 0.2 TiO 3.2 presents promising performance for application in non-volatile memories.
Applied Physics Express, 2011
This paper reports a direct observation of resistive switching occurring on the nanoscale within NiO layers deposited on top of a tungsten pillar bottom electrode. Filamentary conduction was evidenced by atomic force microscopy using a conductive tip that enabled performing electroforming and reset operations at nanoscale. In the low resistive state, it is shown that the current is driven by multiple conductive nanometric regions in agreement with the filamentary conduction models. In the high resistive state, conduction originates from weak residual conductive regions remaining after reset operation. Finally, retention measurements performed at the nanoscale demonstrated the persistence of localized conductive regions after more than 30 days. #